Risk of cancer from HRT is double that of original estimate, study shows

A doctor writes: If you are already on HRT, stopping abruptly is not the answer

The publication of a major analysis in the Lancet, involving combined data from 58 studies and more than 100,000 patients, suggesting the risk of breast cancer from taking HRT is twice that originally thought, will concern many women.

The Collaborative Group on Hormonal Factors in Breast Cancer study focused on the long-term effects of HRT and examined particularly age at first use, duration of use, and time elapsed since last use. It is an intricately designed study.

HRT use has long been linked to breast cancer, and to a lesser extent to ovarian cancer as well. Prescribing fell significantly after the publicity stemming from the Women’s Health Initiative (WHI) trial reports in 2002 and 2004, which showed an increase in the risk of breast cancer with the use of the most common form of HRT – a combination therapy of oestrogen and progesterone.

The latest study found that the longer women take HRT, the greater their risk of developing breast cancer. It also found that the risk does not go away as soon as women stop taking it, as had been previously assumed. However, the study suggests there is no additional risk for women who take HRT for up to a year.


To place the findings in context, the estimated incidence of breast cancer over a 20-year-period was 6.3 per cent for women who never used HRT. For those who used HRT for five years, the incidence was 8.3 per cent – an increase of 2 per cent.

Absolute risk

Rather than focus on relative risk, what does the study say about the absolute risk of developing breast cancer as a result of taking HRT? It found that one in 50 women, of average weight, taking combination HRT for five years, will get breast cancer as a result of the treatment.

Women who take HRT should also ensure they attend for breast screening

So for women weighing up the pros and cons of starting HRT, that is the statistic to focus on. They may also wish to reflect on comments about the research by Sir Richard Peto, professor of medical statistics at Oxford University, who said it showed a cause-and-effect relationship. “It is not just an association that exists, because the menopausal hormone therapy is causing the increase in breast cancer,” he told the Guardian.

Should women currently taking HRT stop in view of these findings? No, abruptly stopping therapy is not the answer. What would be appropriate would be to discuss the personal risks and benefits of HRT with their GP at the next routine appointment. And women who take HRT should also ensure they attend for breast screening.

The menopause can be an unpleasant, and in some cases a disabling experience; HRT is usually effective at improving the symptoms. For those women who wish to continue to take HRT, they should take hormone therapy at the lowest dose and for the shortest possible time that works for them.

Muiris Houston

Dr Muiris Houston

Dr Muiris Houston is medical journalist, health analyst and Irish Times contributor